Synthesis and Exploratory Deposition Studies of Isotetrasilane and Reactive Intermediates for Epitaxial Silicon.

A synthetic method is presented for the production of isotetrasilane, a higher order perhydridosilane, with the purity and volume necessary for use in extensive studies of the chemical vapor deposition (CVD) of epitaxial silicon (e-Si) thin films. The chemical characteristics, thermodynamic properties, and epitaxial film growth of isotetrasilane are compared with those of other perhydridosilanes. A film-growth mechanism distinct from linear perhydridosilanes H(SiH2) nH, where n ≤ 4, is reported. Preliminary findings are summarized for CVD of both unstrained e-Si and strained e-Si doped with germanium (Ge) and carbon (C) employing isotetrasilane as the source precursor at temperatures of 500-550 °C. The results suggest that bis(trihydridosilyl)silylene is the likely deposition intermediate under processing conditions in which gas-phase depletion reactions are not observed.

An unusual bis-heteroscorpionate complex with anomalous ligands: [tris(3,4-dibromo-5-phenylpyrazolyl)hydroborato][hydrotris(3-neopentylpyrazolyl)borato]nickel(II).

Tridentate trispyrazolylborate (Tp) ligands, introduced by Trofimenko in 1966, have been widely utilized in metal coordination chemistry because of the relatively facile synthetic modification of their electronic and steric factors. The title heteroscorpionate, [Ni(C27H16BBr6N6)(C24H40BN6)], features one ligand, namely hydrotris(3-neopentylpyrazolyl)borate, that has previously displayed variable steric effects, and a brominated ligand, namely tris(3,4-dibromo-5-phenylpyrazolyl)hydroborate, that, atypical in trispyrazolylborate chemistry, coordinates such that the less bulky pyrazole substituent is oriented facing toward the metal ion. The potential molecular threefold symmetry in scorpionates can allow axial chirality. Although crystallized in the centrosymmetric P-1 space group, a closer inspection of the structure of the title compound reveals axial diastereomers.

A family of four-coordinate iron(II) complexes bearing the sterically hindered tris(pyrazolyl)borato ligand Tp(tBu,Me).

A new family of 14-electron, four-coordinate iron(II) complexes of the general formula [Tp(tBu,Me)FeX] (Tp(tBu,Me) is the sterically hindered hydrotris(3-tert-butyl-5-methyl-pyrazolyl) borate ligand and X=Cl (1), Br, I) were synthesized by salt metathesis of FeX(2) with Tp(tBu,Me)K. The related fluoride complex was prepared by reaction of 1 with AgBF(4). Chloride 1 proved to be a good precursor for ligand substitution reactions, generating a series of four-coordinate iron(II) complexes with carbon, oxygen, and sulphur ligands. All of these complexes were fully characterized by conventional spectroscopic methods and most were characterized by single-crystal X-ray crystallographic analysis. Magnetic measurements for all complexes agreed with a high-spin (d(6), S=2) electronic configuration. The halide series enabled the estimation of the covalent radius of iron in these complexes as 1.24 Å.

Sterically bulky tris(triazolyl)borate ligands as water-soluble analogues of tris(pyrazolyl)borate.

The recently synthesized 3-tert-butyl-5-methyl-1,2,4-triazole reacted with KBH4 to give the new potassium tris(3-tert-butyl-5-methyl-1,2,4-triazolyl)borate K(Ttz(tBu,Me)) ligand. Ttz(tBu,Me) formed a four-coordinate (Ttz(tBu,Me))CoCl complex and five-coordinate (Ttz(tBu,Me))CoNO3 and (Ttz(tBu,Me))ZnOAc complexes. When these complexes were compared to their Tp(tBu,Me) analogues, it was found that Ttz(tBu,Me) resulted in negligible steric differences. K(Ttz(tBu,Me)) is more water-soluble than K(Tp(tBu,Me)), so bulky tris(triazolyl)borate ligands should lead to functional models for enzyme active sites in an aqueous environment and the creation of water-soluble analogues of Tp catalysts.

Unusual polybrominated polypyrazolylborates and their copper(I) complexes: synthesis, characterization, and catalytic activity.

Five new homoscorpionate ligands were prepared and structurally characterized as their Tl complexes, three of which, Tl[TpBr,Ph,Br] (1) (Tp = hydrotris(pyrazolyl)borate, Tl[TpBr,p-Tomicronl,Br] (2), and Tl[TpBr,p-ClPh,Br] (3), are unique in being the first examples of an "atypical" B-N bond to the most sterically hindered pyrazole nitrogen. They contain bromine atoms on the central and outer carbons of the pyrazole ring, with all aryl substituents in the 5-position of the ligand, forming a protective pocket around the B-H bond. These complexes display a rather high B-H stretch frequency (above 2 600 cm-1) in the IR region. Two other ligands, Tl[Tpp-ClPh,4Br] (4) and Tl[TpPh,Me,Br] (5), containing no outer bromine substituents, have normal B-N bonding to the least-hindered nitrogen. These new ligands have been employed to prepare the series of complexes TpxCu(NCMe) (6-10), for which X-ray studies of two of them (7 and 10) have shown that the atypical or normal geometry of the ligands is maintained when complexed to the copper center. The new complexes have also been tested as the catalysts in carbene and nitrene transfer reactions providing moderate to high yields in the expected products.

Synthesis of zinc, copper, nickel, cobalt, and iron complexes using tris(pyrazolyl)methane sulfonate ligands: a structural model for N,N,O binding in metalloenzymes.

Ligands of intermediate steric bulk were designed to mimic metalloenzymes with histidine and carboxlyate binding sites. The reaction between tris(3-isopropylpyrazolyl)methane and butyllithium followed by SO3NMe3 in THF yielded the new ligand lithium tris(3-isopropylpyrazolyl)methane sulfonate (LiTpmsiPr). Various metal salts reacted with LiTpmsiPr to give the octahedral complexes M(TpmsiPr)2 (M = Zn, Cu, Ni, Co, Fe) in which each ligand has N,N,O binding to the metal. In the reaction between LiTpmsiPr and ZnCl2, in addition to the major product Zn(TpmsiPr)2, [LiTpmsiPrZnCl2].2THF was also formed as a minor product with a tetrahedral zinc atom coordinated to either N,N,Cl,Cl in the solid phase or N,N,N,Cl in acetonitrile solution. Although TpmsiPr is coordinatively flexible and can act as a bipodal or tripodal ligand, it appears to favor the formation of octahedral L2M complexes.

Glycogen synthase kinase-3beta haploinsufficiency mimics the behavioral and molecular effects of lithium.

Lithium is widely used to treat bipolar disorder, but its mechanism of action in this disorder is unknown. Several molecular targets of lithium have been identified, but these putative targets have not been shown to be responsible for the behavioral effects of lithium in vivo. A robust model for the effects of chronic lithium on behavior in mice would greatly facilitate the characterization of lithium action. We describe behaviors in mice that are robustly affected by chronic lithium. Remarkably, these lithium-sensitive behaviors are also observed in mice lacking one copy of the gene encoding glycogen synthase kinase-3beta (Gsk-3beta), a well established direct target of lithium. In addition, chronic lithium induces molecular changes consistent with inhibition of GSK-3 within regions of the brain that are paralleled in Gsk-3beta+/- heterozygous mice. We also show that lithium therapy activates Wnt signaling in vivo, as measured by increased Wnt-dependent gene expression in the amygdala, hippocampus, and hypothalamus. These observations support a central role for GSK-3beta in mediating behavioral responses to lithium.